Conventional web converting equipment uses some sort of transport mechanism for moving the web at high rates of speeds through a series of processing stations. Typically such processing stations includes corrosive environments through which the web must be transported. For instance, in existing photographic film processors used to develop and fix photosensitive elements which are subjected to x-ray, visible and other radiation, the web is transported via a series of rollers defining a web transport path through a sequence of processing stations and then on to final processing in which the web is washed and then dried.
Moreover, process and transport apparatus for photosensitive or other media are other well known applications requiring a web transport mechanism. Such equipment may include automatic processing of the media for thermal, ink jet or silver halide-based photographic printing, and the like. The apparatus automatically transports sheets or webs or strips of photosensitive films, photosensitive papers or specially coated papers or plain papers. For photosensitive elements, this apparatus transports from a feed end of a film transport path, through a sequence of chemical processing tanks in which the media is developed, fixed, and washed, and then through a dryer to a discharge or receiving end. The processing equipment typically has a fixed film (media) path length, so final image quality depends on factors including transport speed which determines length of time the media is in solution, and the temperature and composition of the processing chemicals.
Generally speaking, majority of the components that are exposed to harsh chemicals in a photographic film processor or a thermal printer or an ink jet printer are made from AISI 300 series stainless steel or engineering plastic for reasons of mechanical strength, lower cost, and relatively good corrosion resistance. Engineering plastics are generally used as bushings and gears because of their relatively low coefficient of friction against stainless steel. Furthermore, photographic transport apparatus exposed in normal ambient conditions are also prone to wear and corrosion because of the abrasive and corrosive nature (depending on their relative humidity) of the photographic elements. Although stainless steel shafts have considerable strength and corrosion resistance, yet they are prone to wear with time and are also susceptible to corrosion when come in contact with harsh chemicals which are used in "fixer" solution for developing photographic films. Many engineering plastics are reinforced with glass and carbon fibers or other hard inorganic particles to improve the strength and wear resistance at the expense of proneness to corrosion. Another problem arises with plastic components in a fluid environment is that they tend to swell and become dimensionally unstable. For the reasons mentioned above, it is apparent that there is a need for materials which will endure the harsh chemical environments and at the same time will be compatible with other components of the system thereby enhancing the service life of the transport apparatus.
Experience indicates that structural ceramics like silicon carbide, alumina, zirconia and zirconia-alumina composites offer many advantages over conventional engineering materials, especially metals and plastics, to form bushings, gears and shafts, including many other ceramics and ceramic-metal composites (also referred to as cermets). It is to be noted that an ideal material combination for shafts bushings and gears is to be made so that the assemblage works synchronously and provides a longer service life. Many ceramics and cermets are hard and as a result are wear resistant. It is impossible to be speculative as to what material combinations would work functionally well as a bushing-shaft-gear assemblage. Although ceramic is relatively brittle, it can be used as a bushing in appropriate combination with other engineering materials. Alumina, alumina-toughened zirconia, zirconia and zirconia-toughened alumina ceramic sleeves over stainless steel shafts or solid ceramic shafts worked very well in conjunction with silicon carbide bushings. Incorporation of ceramic bushings in combination with ceramic shafts rendered the assemblage wear resistant and durable making the gear assembly the weakest link. It was surprisingly observed that precision ceramic gears made from Y-TZP or alumina-toughened zirconia were very compatible with the ceramic shaft-bushing assembly thereby making the assemblage more durable and efficient.
It is further known that a moving assemblage having a bearing surface in rotating contact with a stationary shaft or vice versa has a longer service life and better performance if made with not only a hard material but also the mating surfaces have low coefficient of friction.
It is also known that a gear assembly having sliding and rotating contact with the mating surfaces have a longer service life and a better performance if made with a hard material and the mating surfaces have low sliding (kinetic) coefficient of friction.
It is further known that a moving assemblage having a bearing surface in rotating contact with a stationary shaft or vice versa has a longer service life and better performance if made with not only a hard material but also the mating surfaces have low rotating (kinetic) coefficient of friction.
It is also know that a gear assembly having sliding and rotating contact with the mating surfaces have a longer service life and a better performance if made with a hard material and the mating surfaces have low coefficient of sliding or rotating friction.
As will be more completely disclosed, the method of our invention applies to a transport apparatus, i.e., a complete set of stationery bearing and rotating shaft made of ceramics or a complete set of rotating bushing and stationary shaft made of ceramics, particularly one member of assemblage made of silicon carbide. As will be more disclosed, the film processing equipment also utilizes ceramic gears made of Y-TZP and alumina-toughened zirconia (ATZ) ceramics. Proper choices of ceramics in manufacturing these bearings are essential to overcome the problems described above.
Therefore, a need persists for a media transport apparatus equipped with ceramic bushing/shaft assemblage that has superior wear and abrasion and corrosion resistance while being cost-effective and easy to manufacture. A need also persists to use ceramic gears in conjunction with ceramic bushing/shaft assemblage that has superior wear and abrasion and corrosion resistance and manufactured using net-shape technology.